1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and its production method.
2. Description of the Related Art
With the recent tendency toward high-performance central processing unit (CPU) of personal computer (PC), it is desired to develop solid electrolytic capacitors having a reduced ESR (equivalent series resistance) in a high-frequency region. ESR depends on cathode conductivity and, in a case of multilayered cathode lamination, it depends on the contact resistance between the cathode layers.
In general, a solid electrolytic capacitor comprises a porous anode formed of a valve metal or its alloy and a dielectric layer formed on the surface in the inside part or the outer peripheral part of the anode through anodic oxidation thereon, in which an electrolyte layer is provided on the dielectric layer, and a cathode is formed thereon. JP-A 4-48710 proposes formation of a conductive polymer film containing an aromatic sulfonic acid anion as a part of dopant therein on a dielectric layer through chemical polymerization, and additional formation of a conductive polymer film thereon through electrolytic polymerization.
JP-A-Hei-10-321471 proposes formation of a first conductive polymer layer of polythiophene or its derivative followed by formation thereon of a second conductive polymer layer through electrolytic polymerization of polypyrrole or its derivative, and use of these as electrolyte layers.
However, even the methods proposed by these prior-art techniques could not sufficiently reduce ESR.